I often only do enough to finish my homework and read ahead for Biology, so rarely more than ninety minutes worth of work (and how my A2 timetable has fallen I can often just do this in my frees).
In AS, after about April I was doing four hours after school, homework + revision. I also often did 40-50 minutes before my first lesson (I'd come into school earlier).
Weekend, I only finish homework if I need to. AS, after April I'd put in two/three hours on Saturday, maybe four/five on Sunday.
As I got closer to AS exams (mid-May time) though, I was probably getting about six hours after school, homework + revision, and just over an hour before my first lesson.